1. Field of the Invention
The present invention relates to a gas separation membrane, a method of producing a gas separation membrane, a gas separation membrane module, and a gas separator. More specifically, a first aspect and a fourth aspect of the present invention relate to a gas separation membrane which has gas separation selectivity under high pressure, a method of producing the gas separation membrane, a gas separation membrane module having the gas separation membrane, and a gas separator having the gas separation membrane module. More specifically, a second aspect of the present invention relates to a gas separation membrane in which at least one of gas permeability or gas separation selectivity is high under high pressure and bending resistance is excellent, a gas separation membrane module having the gas separation membrane, and a gas separator having the gas separation membrane module. Still more specifically, a third aspect of the present invention relates to a gas separation membrane in which at least one of gas permeability or gas separation selectivity is high under high pressure and pressure resistance is excellent, a gas separation membrane module having the gas separation membrane, and a gas separator having the gas separation membrane module.
2. Description of the Related Art
A material formed of a polymer compound has a gas permeability specific to the material. Based on this property, it is possible to cause selective permeation and separation out of a target gas component using a membrane formed of a specific polymer compound (gas separation membrane). As an industrial use aspect for this gas separation membrane related to the problem of global warming, separation and recovery from large-scale carbon dioxide sources with this gas separation membrane has been examined in thermal power plants, cement plants, or ironworks blast furnaces. Further, this membrane separation technique has been attracting attention as a means for solving environmental issues which can be achieved with relatively little energy. In addition, the technique is being used as a means for removing carbon dioxide from natural gas mainly including methane and carbon dioxide or biogas (biological excrement, organic fertilizers, biodegradable substances, sewage, garbage, fermented energy crops, or gas generated due to anaerobic digestion).
The following methods are known to be used for securing gas permeability and gas separation selectivity by making a site contributing to gas separation into a thin layer to be used as a practical gas separation membrane. A method of making a portion contributing to separation serving as an asymmetric membrane into a thin layer which is referred to as a skin layer, a method of using a thin film composite provided with a selective layer contributing to gas separation which is disposed on a support having mechanical strength, or a method of using hollow fibers including a layer which contributes to gas separation and has high density is known.
As typical performances of a gas separation membrane, a gas separation selectivity shown when a target gas is obtained from a mixed gas and a gas permeability of a target gas are exemplified. For the purpose of enhancing the gas permeability or gas separation selectivity, gas separation membranes having various configurations have been examined.
For example, JP1986-54222A (JP-S61-54222A) describes a method of enhancing gas separation selectivity of a mixed gas of carbon dioxide and methane using a gas separation membrane having a configuration in which a non-porous interlayer containing a compound having a siloxane bond is provided on a porous support and a layer containing cellulose triacetate or polyimide is provided thereon.
JP1985-139316A (JP-S60-139316A) described a method of producing a laminated composite membrane for gas separation having high selectivity (gas separation selectivity) in which a low-temperature plasma treatment is performed on the surface of a composite membrane for gas separation using a non-polymerizable gas and a thin layer of a silicon-containing polymer such as a compound having a siloxane bond is formed on the surface subjected to the plasma treatment. In this literature, polydimethylsiloxane is exemplified as a gas separation composite membrane on which a low-temperature plasma treatment is performed. In this literature, argon or the like is exemplified as a non-polymerizable gas used for the low-temperature plasma treatment. Further, in each example of this literature, only an example of performing the low-temperature plasma treatment on the surface of the composite membrane for gas separation which is formed of a polydimethylsiloxane copolymer using argon gas as the non-polymerizable gas is described.
JP1991-8808B (JP-H03-8808B) describes a composite membrane in which a thin membrane formed of a siloxane compound having a specific structure is laminated on a polymer porous support and a plasma polymerization membrane is laminated thereon, and only the surface layer of the thin membrane formed of a siloxane compound is subjected to a plasma treatment using a non-polymerizable gas. Further, this literature further describes that the composite membrane having such a configuration has excellent gas selection permeability (high gas separation selectivity and high gas permeability).
JP2013-75264A describes a method of providing a hydrophilic modification treatment surface having a film thickness of 0.1 μm or less on the surface of the layer having separation selectivity by performing a UV ozone irradiation treatment and a silane coupling agent treatment carried out after the UV ozone irradiation treatment, in a thin film composite including a support and a layer which is formed of polydimethylsiloxane and has separation selectivity. The examples of this literature describe that the film thickness of the hydrophilic modification treatment surface provided on the surface of the layer having separation selectivity is in a range of approximately 1 nm to 21 nm and gas permeability is degraded when the film thickness is extremely large.
Moreover, this literature describes a plasma treatment together with the UV ozone irradiation treatment as an example of the hydrophilic modification treatment, but an example of using the plasma treatment is not described in the examples of this literature. Further, this literature describes a method of introducing a gas mainly including argon gas into a process chamber and performing an atmospheric pressure plasma treatment, as an example of the plasma treatment.
Journal of Membrane Science 99 (1995) pp. 139 to 147 describes that, when the surface of a membrane formed of a polyimide support and polydimethylsiloxane is treated at a low power of 5 W or less in the order of minutes (during 120 seconds), the ratio of permeability of carbon dioxide relative to the permeability of methane is increased compared to the original polydimethylsiloxane under atmospheric pressure after 30 minutes from the treatment, but high gas separation selectivity has not been obtained.
Journal of Membrane Science 440 (2013) pp. 1 to 8 describes that, when the surface of a polydimethylsiloxane film is subjected to a plasma treatment at a high temperature under atmospheric pressure, the ratio between oxygen atoms and silicon atoms in the surface is increased by 1.6, but high gas separation selectivity has not been obtained.